Optoelectronic devices are used for a variety of different industrial, military, and consumer purposes. Typical optoelectronic devices include an emitter, such as a light emitting diode (LED), and a receiver, such as a photodiode. In operation, an electromagnetic signal (e.g., light beam) is generated by the LED and directly or indirectly received by the photodiode. In practice, a number of configurations may be used for detecting items, including a through-beam configuration, retro-reflective configuration, and proximity-sensing configuration. The through-beam configuration includes an emitter and receiver pair, where the emitter directly illuminates the receiver with an electromagnetic signal. When an item breaks a line-of-sight between an emitter and receiver, the electromagnetic beam is not sensed by the receiver, and detection of the item is made. A retro-reflective configuration is configured with an emitter and receiver typically positioned in a single housing, and where the emitter illuminates a reflector, such as a mirror, that reflects an incident electromagnetic signal onto the receiver. Responsive to the receiver receiving the reflected electromagnetic signal, a determination is made as to whether a change to the reflected electromagnetic signal occurred or whether the electromagnetic signal is blocked completely. A proximity-sensing configuration has an emitter and receiver typically in a single housing, and the emitter outputs an electromagnetic signal onto items as the items enter into a path of the electromagnetic signal. The receiver senses a reflected electromagnetic signal from the item, as opposed to a reflector as with the retro-reflective configuration. The receive signal may be produced at a magnitude commensurate with amplitude or intensity of the reflected electromagnetic signal.
In operation, the receiver (e.g., photodiode) generates a receive signal indicative of receiving an incident electromagnetic signal on the photodiode. Examples of systems that use optoelectronic devices as described above include manufacturing systems that sense existence (through-beam configuration) and integrity (retro-reflective configuration) of a product, automatic garage doors (through-beam configuration) that sense an obstruction of a garage door while closing, robotics that detect objects (proximity configuration) to be grasped, and many other configurations and uses.
One particular sensing task that is difficult for optoelectronic sensing systems to perform includes sensing transparent and/or shiny objects. Such transparent and/or shiny objects include, but are not limited to, clear plastic products (e.g., beverage glass or plastic bottles), products package with clear plastic (e.g., medicines, foods, an other consumer goods), and so forth. For sensing transparent and/or shiny objects, retro-reflective sensing may be used as the reflection of an altered electromagnetic signal is indicative of the transparent and/or shiny objects being positioned between an emitter/receiver pair and reflector, as understood in the art.
Where optoelectronic systems are used to sense transparent and/or shiny objects, polarized electromagnetic or optoelectronic signals may be used. Polarized electromagnetic signals are produced by causing a transverse electric field to be aligned in one direction as opposed to being random or scattered, as understood in the art. An optoelectronic receiving device may be aligned to receive the electromagnetic signal with the polarization filter positioned in front of the electromagnetic receiving device so that if the filter allows the polarized electromagnetic signal to pass with a first, high signal strength, then a determination may be made that the electromagnetic signal has not been altered. Otherwise, if the received electromagnetic signal is received at a second, lower signal strength, then it is determined that an object, in this case a transparent and/or shiny object, is detected due to the polarized electromagnetic signal being rotated such that the filter causes the lower signal of the electromagnetic signal to be sensed by the optoelectronic device.
A variety of optoelectronics system configurations have been used by conventional systems, including configurations with multiple optoelectronic emitters that turn on and off to utilize distinct polarization, multiple polarized filters, rotating polarized filters, and so forth. These optoelectronic systems, however, are expensive, complex, and use additional space. Traditional detectors are generally calibrated with a single polarization configuration, so these detectors are to be adapted manually to the type of object being detected. Such manual calibration is time consuming and expensive.
In the case of using multiple polarizing filters, one at the transmitter and one at the receiver rotated 90° from one another, shiny and/or transparent objects may be a problem. In other configurations, the filters and/or other components may be electromechanically rotated so as to provide for different polarizations of the electromagnetic signal. However, electromechanical rotation of physical devices may be slow. The use of microelectronic machines (MEMS) devices may be faster, but cost and space issues still exist. Accordingly, a system that addresses the above-describe shortcomings for optoelectronic sensing systems is needed.